The fabrication of microcircuit devices on a semiconductor wafer involves a number of steps where patterns are transferred from photolithographic masks on the wafer. The masking step includes an etching step and defines selected areas to be exposed on the wafer for subsequent processes such as oxidation, metal deposition and impurity introduction.
In the production of integrate circuit structures, structures have a plurality of layers due the ever increasing density of the circuit elements in the structure. Further, as the device and feature sizes becoming smaller, there is a need to align the photolithographic mask precisely with the wafer during the masking step to minimized the misalignment between the layers